The short answer: typically every 12 months
For most general-purpose digital multimeters used in light to moderate duty (electrical trades, workshop verification, occasional testing), the calibration interval is 12 months. That is the manufacturer default for almost every quality DMM brand and the default starting point most ISO 9001 quality systems use.
A 12-month interval is a balance between two real risks: drift over time (instruments are not perfectly stable) and the cost and downtime of unnecessary calibration. For a typical multimeter, 12 months keeps drift within published accuracy on the day you trust the reading — without making calibration the most expensive line item on your QA budget.
What 12 months is actually based on
Multimeter manufacturers publish a 1-year accuracy specification — for example, “DC volts: ±(0.025% + 2 counts) for 1 year, 23 °C ± 5 °C”. That number assumes the meter has been calibrated within the last 12 months. Once you go past that interval, the manufacturer makes no claim about the meter being in spec, and you cannot defend the reading against the published accuracy.
Some higher-grade multimeters publish a 2-year accuracy spec separately. If you genuinely run on the 2-year spec (a lab bench DMM that lives in a stable environment) you can extend the calibration interval to match — but you must use the 2-year accuracy figure on every test report from that meter, which is usually wider than the 1-year figure.
When to calibrate more often than 12 months
Plenty of real-world conditions justify a shorter interval. The point of risk-based calibration is to match the interval to the failure consequences and the environment, not to apply 12 months as a default that ignores how the meter is used.
- Safety-critical use — for example, a multimeter or clamp meter used to verify a lockout. Shorten to 6 months and consider in-service verification between calibrations.
- High-volume use — meters used dozens of times per day drift faster than meters used occasionally.
- Harsh environment — mine sites, outdoor construction, hot or vibration-heavy workshops. Shorten to 6–9 months.
- After a drop, shock or visible damage — calibrate immediately, before the next critical reading.
- When readings disagree with a second known-good instrument — calibrate to find out which one drifted.
- When your SPC or QC data shows the meter is the source of variation — that is the signal to shorten the interval.
When you can extend the interval
A small number of meters genuinely fit a longer interval. The conditions are narrow but worth knowing.
- The meter has a published 2-year accuracy spec and you genuinely use it within that spec.
- Use is light and infrequent (a few times per month).
- Environment is benign — a controlled workshop or laboratory.
- You have an in-house verification programme that checks the meter against a known reference between calibrations, and the verification data is stable.
How an interval is decided in an ISO 9001 quality system
ISO 9001 (clause 7.1.5 in the 2015 standard) does not prescribe a calibration interval. It does require you to have a process for determining intervals, recording the basis and reviewing them as you collect data. A reasonable defensible position is: start with the manufacturer interval, adjust based on use, environment and consequence, document the rationale, and revise on a defined cycle (annually is common).
If your QMS is audited, an auditor will not argue with 12 months for a typical DMM — but they will ask how you decided the interval. Having the rationale written down is the part most teams miss.
What you can do between calibrations
Between formal calibrations, you can run sensible in-service checks: zero the meter on a shorted lead, compare against a second meter on a known voltage source, and check ranges you actually use. These verify the meter is still behaving — they are not a substitute for a traceable calibration. Document any verification check you rely on; if the auditor asks, you want to point at the record.
What a Perth calibration of a multimeter actually involves
When AmpTech calibrates a multimeter in our Caversham lab, we run the meter through points across each range it is used on — DC and AC volts, DC and AC current, resistance, frequency and continuity — using reference instruments traceable to national standards. Each point is recorded as as-found and as-left, so you can see what the meter read before any adjustment and where it sits after.
You receive a calibration certificate with the equipment under test, the reference instruments used, environmental conditions, the as-found / as-left readings and a traceability statement. We then set a recall reminder so you know when the next calibration is due. Getting the meter to us is up to you: drop it at the lab, or book our pickup & drop-off service.